Domestic kittens: individual differences in separation calls and locomotor activity across age. (a-d) Separation calls. Consistent individual differences in the number of calls during four, 3-minute separation tests across the first postnatal month. (e-h) Locomotor activity. Weaker consistency in individual differences in the % time the animals spent showing locomotor activity during the four tests, with no significant correlation (h) between individual differences in the first and the final week. Each circle gives the score for an individual kitten (n = 33 / 8 litters). Note that the association depicted in (h) is not statistically significant; see text for details of statistics.